1. Field of the Invention
The present invention relates to an optical disk drive and optical pickup, which irradiate an information-recording medium such as CD and DVD with a light beam, for performing information reproduction or recording, and in particular, it relates to an improvement of aberration correction in the pickup which is mounted on this optical disk drive.
2. Description of the Related Art
Conventionally, there has been a problem of deterioration in performance of a pickup mounted on an optical disk drive or the like, which performs reproduction or recording from/on an optical disk such as DVD. Such deterioration is caused by an influence of wavefront aberration generated by various factors.
For instance, the wavefront aberration includes coma aberration caused by tilted angle of the optical disk, spherical aberration caused by a difference in substrate thickness of the optical disk, and the like. The coma aberration and the spherical aberration mentioned above are dynamic aberrations which fluctuate along with driving of the optical disk drive. In addition to those dynamic aberrations, there also exists a static astigmatism caused by an optical system. This static astigmatism occurs due to errors such as precision errors and assembling errors in optical components. Therefore, there is a characteristic that even if a pickup includes an optical system of the same configuration designed by the same specification, astigmatism in each pickup may be different in direction and size. In order to correct this astigmatism, there has been proposed an aberration correcting apparatus. In this aberration correcting apparatus, a liquid crystal element is placed within an optical path in the pickup, refraction index of the liquid crystal is changed by applying voltage on this liquid crystal element, and the astigmatism is corrected by giving a phase difference to a light beam passing through the liquid crystal element (for example, see the Japanese Patent Laid-open Publication No. 2000-40249, Page 5, FIG. 1 and the Japanese Patent Laid-open Publication No. Hei-11-259892 (1999-259892), FIG. 5, hereinafter, referred to as Patent Document 1 and Patent Document 2, respectively).
Hereinafter, a related art disclosed by the Patent Document 1 will be explained with reference to the accompanying drawings. FIG. 14 is a block diagram showing a configuration of the optical pickup mounted on a conventional optical disk drive.
In FIG. 14, the optical pickup comprises a laser light source 41, polarized beam splitter 42, liquid crystal element 43 functioning as an astigmatism correcting means, quarter wavelength plate 44, objective lens 45, condenser lens 46, optical receiver 47, and liquid crystal element controller 48. In addition, the optical disk 50 that is irradiated with a light beam by the optical pickup is designed to be rotationally driven by a spindle motor 49. Here, the light beam 51 emitted from the laser light source 41 passes through the polarized beam splitter 42, and the light beam 51 is incident onto the liquid crystal element 43, further passes through the quarter wavelength plate 44, and the light beam is focused on the information recording surface of the optical disk 50 by the objective lens 45.
In other words, the liquid crystal element 43 is placed in passage area of the light beam 51. This liquid crystal element 43 is driven by means of liquid crystal element controller 48 to correct astigmatism. On the other hand, the light beam 51 is reflected from the information recording surface of the optical disk 50, and again, the light beam passes through the objective lens 45 and the quarter wavelength plate 44 in this order. Then, the optical path is changed by the polarized beam splitter 42, and the light beam is focused on the optical receiver 47 through the condenser lens 46. The optical receiver 47 converts the received optical signal to an electrical signal, and outputs thus converted signal.
Next, FIG. 15 shows an electrode structure of the liquid crystal element 43.
In FIG. 15, reference numeral 52 indicates an incident range of the light beam 51. The liquid crystal element 43 is divided into nine pattern electrodes 53a to 53i within this incident range 52. In other words, a circular pattern electrode 53a is formed in such a manner as being associated with the center portion of the incident range 52. In addition, eight pattern electrodes 53b to 53i, radially divided, are formed on the outer periphery of the incident range 52. Accordingly, the eight pattern electrodes 53b to 53i are divided almost equiangularly about the center of the incident range 52, and arranged symmetrically.
The pattern electrodes 53b, 53c, 53d, and 53e are respectively facing to 53f, 53g, 53h, and 53i, being arranged centrosymmetrically. With this arrangement of the pattern electrodes, it is possible to handle a particular direction of the astigmatism. A drive pattern of the liquid crystal element 43 is determined by voltages applied to a plurality of pattern electrodes 53a to 53i. The voltages applied to the pattern electrodes 53a to 53i are determined according to the direction and size of the astigmatism, whereby it is possible to correct the astigmatism by providing a phase difference to the light beam 51 passing through each divided area. As thus described, according to the disclosure by the Patent Document 1, the astigmatism caused by the optical system of the optical pickup can be corrected. Therefore, optical components do not need necessarily to be with an extremely high precision, adjustments after assembling are not required either, and thus it is possible to correct the astigmatism of the optical pickup favorably.
As one of another conventional arts, there is proposed a pickup unit which has a built-in control circuit, and this built-in control circuit controls the laser light source, photo-transformation element, the liquid crystal element and the like prepared for aberration correction (see Japanese Patent Laid-open Publication No. 2003-346375, Page 4, FIG. 1, hereinafter referred to as Patent Document 3). Hereinafter, the conventional art disclosed in the Patent Document 3 will be explained with reference to the accompanying drawings. FIG. 16 is a block diagram showing a schematic configuration of a conventional pickup unit and an optical disk drive on which this pickup unit is mounted.
In FIG. 16, the optical disk drive 60 is an apparatus which records information on various optical disks such as DVD-R and DVD-RW, and reproduces the information being recorded. FIG. 16 shows only a pickup unit 61 and a main substrate 70 electrically connected to the pickup unit 61 within the optical disk drive 60.
The pickup unit 61 is provided with optical system components 62 including objective lens and the like, electrical components 63 including laser diode as a laser light source, photo-transformation element, liquid crystal element, and driver, and control circuit 64 including a small-scale microcomputer and the like. Those constituent elements are arranged on a flexible substrate 65. In addition, a connector 66 is installed on the edge of the flexible substrate 65. On the other hand, a microcomputer 71 for controlling the entire operations of the optical disk drive 60, and a recording signal generator 72 which generates data to be recorded on the optical disk (not illustrated) are arranged on the main substrate 70. The microcomputer 71 in the main substrate 70 and the connector 66 in the pickup unit 61 are electrically connected via a signal line 73. The recording data which the recording signal generator 72 has generated is transmitted to the pickup unit 61 via a signal line 74 which is provided separately from the signal line 73.
In the above configuration, the microcomputer 71 in the main substrate 70 transmits various control commands to the control circuit 64 in the pickup unit 61 via the signal line 73. The control circuit 64 executes various controls on the electrical components 63 according to the control commands from the microcomputer 71. The control circuit 64 including a small-scale microcomputer and the like, being provided within the pickup unit 61, performs control of the electrical components 63 built in the pickup unit 61, without depending on the microcomputer 71 provided externally. Accordingly, it is possible to shorten the signal line between the electrical components 63 and the control circuit 64, and influences of noise generated from the signal line can be suppressed. In addition, the pickup unit 61 can be downsized with the shortened signal line. As for the microcomputer 71 of the main substrate 70, it is only required to output a control command to the control circuit 64 in the pickup unit 61, and thus loads onto the microcomputer 71 can be reduced.
Furthermore, there is also known a conventional art which corrects spherical aberration of an optical pickup (see Japanese Patent Laid-open Publication No. 2003-257069, FIG. 1, hereinafter referred to as Patent Document 4). The conventional art disclosed in the Patent Document 4 will be explained with reference to the accompanying drawings. FIG. 17 is a block diagram showing a schematic configuration of a conventional optical pickup unit and a drive substrate.
In FIG. 17, the optical pickup 81 is provided with an optical system 85 which performs light irradiation and light acceptance on/from a recording medium (not illustrated), an objective actuator 82 which drives an objective lens (not illustrated), an expander actuator 83 which drives an expander lens, and a memory means 84. The expander lens corrects the spherical aberration, by changing lens spacing. Furthermore, the memory means 84 stores a drive voltage of the expander actuator 83.
Drive substrate 91 is provided with a drive controller 94 for controlling the device entirely, an objective actuator driver 92 which drives the objective actuator 82 under the control of the drive controller 94, and a lens driver 93 which drives the expander actuator 83 under the control of the drive controller 94.
The drive controller 94 reads a value of the spherical aberration correction voltage stored in the memory means 84. Then, the drive controller 94 adds the value of the spherical aberration correction voltage having been read out to the drive voltage of the expander lens, and after that, transmits to the lens driver 93 a command to actuate the expander actuator 83.
By adding the stored value of the spherical aberration correction voltage to the drive voltage of the expander lens, it is possible to shorten the initial processing time required for the spherical aberration correction.
In the pickup units as described in the Patent Documents 1 and 2, however, in order to correct the optical system aberration of individual pickup by use of the liquid crystal element, it is necessary to provide the optical disk drive side with astigmatic data peculiarly held by the pickup, calculate correction data based on this peculiar astigmatic data on the optical disk drive side, and gives a feedback to the pickup side. Therefore, conventionally it has been performed that the astigmatic data peculiar to the pickup is measured individually when a pickup manufacturer produces the pickup, and the pickup manufacturer supplies the data, through various means, to an optical disk drive manufacturer who incorporates the pickup into the optical disk drive.
For example, such various means may include a method which supplies the astigmatic data by attaching a bar code onto a packaging material or the like for packing the pickup, or a method which creates a data table in which astigmatic data is associated with a serial number of the pickup, and supplies the data table together with the pickup. Then, it has been performed that when the optical disk drive manufacturer incorporates the pickup into the disk drive, the individual astigmatic data supplied with the bar code or the data table, is memorized inside the optical disk drive by any means, so as to execute a process to calculate correction data.
However, from a standpoint of the pickup manufacturer, there is a problem that creation of bar code or data table for the astigmatic data may drive up man-hour in manufacturing, resulting in a cost increase. On the other hand, from a standpoint of the optical disk drive manufacturer, the operation for reading the bar code or data table, or the operation for writing the data into the optical disk drive is additionally required. Therefore, in addition to the problem that the manufacturing process may be complicated and workability is lowered, there is a risk that errors may occur such as an error in reading the bar code or the data table, and an error in writing the read-in astigmatic data.
In other words, improvement is now demanded in supplying the astigmatic data from the pickup manufacturer to the optical disk drive manufacturer. Each manufacturing process is required to be simplified to reduce cost, and to enhance reliability by avoiding operational errors or the like, and those are critical issues.
As for the pickup unit as disclosed by the Patent Document 3, the liquid crystal element contained in the optical system components is controlled by a control circuit provided inside the pickup unit, and with this configuration, it is possible to execute the aberration correction. However, there is no consideration as to improvements in a means for supplying the optical disk drive side with the astigmatic data peculiar to the pickup. Therefore, similar to the first example of the related arts, it is necessary to utilize a general supplying means by use of bar code, data table, and the like.
In other words, also in the example of the related arts as disclosed by the Patent Document 3, an improvement is required in supplying the astigmatic data from the pickup manufacturer to the optical disk drive manufacturer.
The information recording/reproducing apparatus as disclosed in the Patent Document 4 corrects a spherical aberration as a type of wavefront aberration, being a dynamic aberration which fluctuates according to driving of the optical disk drive, but it is not intended for correcting the astigmatism being static.
In the technique as disclosed by the Patent Document 4, it is the dynamic aberration which is corrected by a correction process constantly performed while the optical disk is being driven, and it is unknown whether this technique is adequate for correcting the static aberration. In addition, with the expander lens, the spherical aberration can be corrected but the astigmatism cannot be corrected.